Recently, as portable electronic apparatuses have increased in number, a variety of electronic apparatuses have become compact and lightweight. An operating panel switch for the electronic apparatus is low-profile and affords a good click feel and an electrically stable contact, so that a so-called movable contact unit, the insulating resin film of which holds a plurality of separate domed movable contacts formed out of an electrically conductive and resilient metal plate, has found wide use.
To improve operability, the operating panel switch is demanded of an arrangement of keys corresponding to respective switches intended to afford different click feels.
Referring to FIGS. 7-9, a description will be provided hereinafter of a conventional movable contact unit with operating projections that is disclosed in Japanese Patent Laid Open No. 2002-216582.
FIG. 7 is a sectional view of the conventional movable contact unit with the operating projections. Base film 1 is a flexible film of insulating resin. A plurality of domed movable contacts 3 formed out of electrically conductive and resilient sheet metal is bonded to a bottom surface of base film 1 by adhesive layer 2. Separator 4 formed of an insulating film is bonded to the whole bottom surface of base film 1 across movable contacts 3 by adhesive layer 2. The surface of separator 4 is processed for ease of removal. Separator 4 thus formed prevents movable contacts 3 from corroding and also prevents foreign matter from adhering to adhesive layer 2 during transportation and storage.
A plurality of projecting members 5A is each fixed to base film 1 by adhesive resin 5B. These projecting members 5A are formed by stamping a film of resin into cylindrical shapes and hence are circular when viewed from above. Projection member 5A and adhesive resin 5B form operating projection 5.
FIG. 8 shows the thus-constructed movable contact unit with the operating projections that is mounted to an apparatus.
When the movable contact unit with the operating projections is mounted to the apparatus, separator 4 is removed, and base film 1 is bonded to wiring board 7 by adhesive layer 2. Respective central portions of movable contacts 3 each face corresponding central fixed contact 6A across a given clearance, while respective lower borders of movable contacts 3 are each placed on corresponding outer fixed contact 6B. Movable contact 3 and corresponding fixed contact 6 form one switch. Above each operating projection 5, operating button 8 of the apparatus is disposed.
Referring to FIG. 9, a description will be provided next of operation of an operating panel switch using the thus-constructed conventional movable contact unit with the operating projections.
When pressed, operating button 8 moves downward, and downward pushing force is applied accordingly to an upper end of cylindrical projecting member 5A contacting bottom surface 8A of operating button 8. In other words, the pushing force is applied to the central portion of movable contact 3 via projecting member 5A and base film 1. When this pushing force becomes greater than shape retaining force of movable contact 3, domed movable contact 3 is turned inside out while providing the click feel, whereby a bottom surface of its central portion contacts central fixed contact 6A. As a result, central fixed contact 6A and outer fixed contact 6B of wiring board 7 are electrically coupled to each other via movable contact 3.
When released from the pushing force, movable contact 3 restores its original shape with its own resilient restoring force, so that the bottom surface of its central portion departs from central fixed contact 6A. This means that central fixed contact 6A and outer fixed contact 6B of wiring board 7 return to a state in which these contacts 6A, 6B are electrically isolated from each other.
To set operating force (corresponding to the above-mentioned pushing force), which acts on a specified movable contact of the plurality of movable contacts 3, different from operating force which acts on another movable contact of the above-constructed conventional movable contact unit, the following methods are generally conceivable.